1. What is the break point on HP/torque in a B-body that really is getting into the real of unsafe/unstreetable? Entirely up to the driver. I have driven up to 625 n/a or so on the street, And some boosted that went closer to 900. Comfort lays with the drive and the specific car in question. My own opinion, unless you have some really serious suspension and wheels/tires, anything over 550 is wasted cash. Because the car won't be able to handle accelerating with it, or turning with it. Nevermind stopping. Plus the costs go up as a function of output. It costs a lot more to build 600hp reliably in your chassis than is does 500. Anyone who says otherwise probably has a "600hp dyno'd" engine that's not even close to 500hp in their car.
2. What kind of HP/Torque will my set-up theoretically handle? All depends. With an A833, the right clutch, gearing to match the driving habits, and the dana - you can probably do 5-600 without hurting anything. Eventually you'll break the driveline.
3. Similar question around durability... will my RR hold up to 600/600 HP/tq? If not, what do you think may need to be upgraded to handle it? The unibody will need to be reinforced with welded in frame connectors. Beyond that - you can add strength to the nose and firewall with some store-bought parts easy enough. But at that point if the car is honestly solid and done right you won't break anything body-wise.
4. What will my A-833 handle? If you power shift it, it will break down faster. If you put huge tires and a good suspension under it, it will break it. If you drive it normally, and have the right clutch and driveshaft angles, it will last just fine at 600hp.
